Process for electro-development of photographic images



Dec. 10, 1963 M. HEPHER v3,113,910

PROCESS FOR ELECTRO-DEVELOPMENT OF PHOTOGRAPHIC IMAGES Filed June 9, 1960 Fig.1 'W

/SILVER HALIDE-GELHTIN EMULSION LAYER WITH INCORPOIBQTED HYDROQUIMWE //////fi AND SODIUM BISULFITEFORMALDEflYDE I SUPPORT Figz3 Fig: 1

momwsva AGENT United States Patent 3,113,916 PRUQESS l fill ELECTRO-BEVELQPMENT (ll PHEBTQGRAPHHC WAGES Martin Hepher, Wealdstone, Harrow, England, assrgnor to Eastman Kodak Company, Rochester, N.Y., a corporation oi New .lersey Filed June 9, 195 Ser. No. 35,74 16 Claims. (Cl. 2tl42) The present invention relates to photography, more particularly to the development of photographic images in exposed light-sensitive silver halide emulsion layers.

After a light-sensitive silver halide emulsion layer has been exposed to an image to form a latent image in the emulsion layer, it is usual to develop this latent image to form a suitable silver image by treating the layer with a developing solution. The deveioping solutions most widely employed today comprise an organic developing agent, for instance, hydroquinone, an alkali and sodium sulfite. The necessity for the alkali arises from the fact that the developing agents more commonly employed do not develop the latent image unless the pH of the solution is su-fliciently high.

Following development in conventional processes, the emulsion is Washed and then treated with an alkali-metal thiosulfate solution to fix the silver image by removing undeveloped silver halide from the emulsion layer and then the emulsion layer is washed thoroughly to remove the thiosuifate solution.

These processes have the disadvantage of requiring from 4 to 5, steps, each of which usually takes from 5 to minutes. The photographic element is thoroughly water-soaked by this processing procedure and must be dried before it can be handled or used in the normal manner.

it is therefore an object of the present invention to provide a simple rapid method of forming a photographic image in an exposed light-sensitive silver halide emulsion layer.

Another object is to provide a method for forming a photographic image in an exposed light-sensitive silver halide emulsion layer containing an incorporated developing agent and an incorporated electrolyte that is coated on a support, by simply moistening the photographic emulsion layer and support and subjecting it to electrolysis in which the emulsion layer is first brought into contact with the cathode and then into contact with the anode.

Another object is to provide a process for forming a photographic image in an exposed light-sensitive silver halide emulsion layer containing an incorporated developing agent and an incorporated electrolyte and coated on a support by simply moistening the photographic emulsion layer and subjecting it to electrolysis in which a direct electric current is passed between a cathode and an anode that are in contact with the moist emulsion layer as the emulsion layer is drawn past the electrodes in such a way that the exposed emulsion layer is first subjected to the cathode and then subjected to the anode.

Another object is to provide a process for forming a photographic image in an exposed light-sensitive silver halide emulsion layer containing an incorporated developing agent, by simply moistening the photographic emulsion layer and Water-permeable support with an aqueous solution of an electrolyte and subjecting the photographic element to electrolysis in whicha direct electric current is passed between a cathode held in contact with t e surface of the moistened emulsion layer and an anode in contact with the moistened support and subsequently subjecting the emulsion layer to electrolysis in which the direction of current flow is reversed.

3,ll;'i,ld Patented Doc. it), 1%63 Another object of the invention is to provide a process for forming a photographic image in an exposed lightsensitive silver halide emulsion layer by moistening the exposed emulsion layer with an aqueous solution containing a developing agent and an electrolyte and then subjecting the moistened emulsion layer to electrolysis such that the emulsion layer is exposed first to cathodic action and secondly to anodic action.

Still further objects will become apparent from the following description of my invention.

I have found that the above objects and others can be accomplished by using the electrolytic development process of my invention in which a photographic image is produced in an exposed silver halide emulsion layer by electrolysis in the presence of an electrolyte and an organic developing agent. Activation of the developing agent and image formation does not occur until the pH of the developer and electrolyte solution in contact with the emulsion layer is increased sufficiently by hydroxyl ions produced electrolytically by the passage of a direct electric current between a cathode that is brought into contact with the emulsion surface and an anode that is in contact with another part of the photographic material.

Development of the image may be stopped by reversing the direction of current flow. This generates hydrogen ions at the emulsion surface, and thus deactivates the developing agent. When the emulsion is dried and subsequently exposed to light, it will darken in time by the formation of photolytic silver in the unexposed, undeveloped areas of the image. However, the rate of darkening is significantly less when the emulsion is electrolyzed with the polarity reversed, after development. There is also much less tendency to form stains from oxidized developing agent.

In the simplest method of using the invention, a photographic paper coated with a silver halide emulsion which has been exposed to an image is moistened with water and laid emulsion side uppermost on a metal plate which is connected to the positive side of a battery, e.g., a 24-- volt battery and then, providing the emulsion contains at this stage a developing agent such as hydroquinone and preferably a preservative such as sodium bisulfite, it is only necessary to slowly roll across the moist emulsion surface a metal roller which is connected to the negative side of the battery. Although the roller only remains for a very short time in contact with any particular place on the emulsion layer, nevertheless, sufficient electrolysis takes place to raise the pH and the image is immediately developed. The terminal connections between the battery and the plate and the roller can then be reversed, whereupon the roller is passed once again over the layer and in this case the electrolysis occurs again lowering the pH below that at which development can continue.

The incorporation of the developing agent and/ or the electrolyte in the emulsion layer may be carried out during the manufacture of the sensitive paper or by soaking the paper before or after exposure, in a solution containing these substances.

When the developing agent and/or the electrolyte are to be incorporated in the emulsion layer during the manufacture of the sensitive paper and it is necessary to use an incorporating solvent, any of the well known solvent media may be used such as tri-ortho-cresyl phosphate, din-butyl phthalate, etc.

The emulsion layers contain a silver halide or rnixt res of silver halide, e.g., silver chloride, silver bromide, silver iodide, silver chlorobrornide, silver bromoiodide, etc. and may be sensitized or not sensitized as is required by the specific application.

Any of the Well known photographic developing agents useful for developing silver images may be incorporated emulsion layer.

in the emulsion layers used in my process. Among the preferred developing agents are hydroquinone and derivatives of hydroquinone such as methyl phenyl hydroquinone, etc., catechol and derivatives of catechol such as 4-phenyl catechol, etc., derivatives of naphthol such as 4-methoxy-l-naphthol, etc., derivatives of phenol such as methyl p-aminophenol sulfate, etc., the 3-pyrazolidones such as 1-phenyl-3-pyrazolidone.

The electrolytes useful for incorporation in emulsions used in my process or which may be used in solutions for moistening the photographic emulsion immediately before electrolysis are any of the readily water soluble metallic salts of acids which are neutral in their chemical reaction or at least do not have a pH that is high enough to activate the development agent and thus cause photographic development when it is unwanted. Among the salts useful as electrolytes are the alkali-metal sulfites, bisulfites, chlorates, chlorides, sulfates etc. Sometimes it is advantageous to use a development restrainer such as potassium bromide or an antifoggant when an alkali-metal sulfite, or bisulfite is used at the electrolyte in order to prevent the formation of dichroic fog. Dichroic fog may also be prevented by lowering the current density used for the electrolysis. However, the presence of a development restrainer or antifoggant makes voltage control less critical. The use of an alkali-metal bisulfite-formaldehyde addition complex as the electrolyte is particularly advantageous because it is not only a good electrolyte but it does not have the tendency to create dichroic fog as do the alkali-metal sulfites or bisulfites and there is less need to use a development restrainer or antifoggant with the alkali-metal bisulfite-formaldehyde addition complex.

Hydrates of electrolytes such as Na SO 7H20, Na SO 7H O, etc.

may be incorporated in emulsion layers for use in a variation of electrolytic development processes in which the wetting step of the process described above may be eliminated. In this process the passage of the electric current through the emulsion layer releases suflicient water from the hydrated salt to make possible the development of exposed silver halide.

The emulsion layers containing silver halide or mixtures of silver halide, and which may or may not contain incorporated developing agent and an incorporated electrolyte, are coated upon any of the well known suitably subbed supports, however, paper particularly of the highly absorbent type is especially useful. Metal, glass, cellulose esters and other well-known supports may be also used. When metal is used as a support, it is usually subbed with a material such as gelatin, albumin, gum

acacia, etc. Glass, cellulose esters and other transparent materims used as supports may or. may not contain a white pigment to render them opaque. When paper is used for the support, its electrical conductivity may be increased by impregnating it with suitable compounds which when moistened serve as electrolytes. These compounds are usually compounds that have a fair degree of water solubility and which do not exert a detrimental etfect on the stability of the light sensitive emulsion layer 'or upon the developing agent that may be incorporated in the emulsion layer. These compounds are more or less neutral in their chemical reaction or at least insufiiciently alkaline to cause activation of the developing agent in the presence of moisture.

The electrodes used for the electrolysis must be made 'of suitable materials in order that unwanted electrolytic reactions do not occur which might result in the destruction of the electrodes and/or the formation of unwanted discolorations or stains in the processed photographic A very suitable material for the electrodes is stainless steel.

An alternative system, however, depends on the solution of the electrode to form an agent that develops a photographic emulsion. For example, an iron electrode that is made anodic releases ferrous ions to the electrolyte which, in the presence of ethylenediaminietetracetic acid, develops an image in an emulsion that is placed against the anode.

The electrodes may be made in various shapes depending upon the details of the processing equipment that is used. For example, in addition to the electrode design mentioned above, it is advantageous to use rollers for both electrodes in instances where the photographic material to be processed is in strip form and can be drawn continuously between the 2 rollers during the processing operation and at speeds up to 50 feet per minute. The deactivation electrolysis could then be effected by passing the strip of photographic material between a second set of roller electrodes in which the polarity is reversed from that of the first set of rollers. The electrodes may be in the form of blades which are held close together across the surface of the emulsion, This form of electrodes is advantageously used when the light sensitive emulsion is coated on supports which when moistened are either nonconducting or do not have adequate conductivity or when it is desirable to moisten only the emulsion layer of the photographic element during the processing operation.

The accompanying drawings, FIGURESl, 2, 3, 4 and 5 illustrate how the process of my invention is used.

FIGURE 1 shows how the light-sensitive silver halide emulsion layer 12 containing incorporated hydroquinone and sodium bisulfite-formaldehyde addition complex, coated on support 13 is exposed to the image in layer 11 by light source 10.

FIGURES 2, 3 and 4 illustrate different methods of carrying out the electrolytic development of the latent image produced in emulsion layer 12 on support 13 of FIGURE 1 to produce the developed image shown in emulsion layer 12 of FIGURE 5. In each instance the exposed photographic element is first wet with water before being electrolyzed.

In FIGURE 2, the latent image in emulsion layer 12 or" the moistened photographic element placed support down on stainless steel anodic plate 15 is developed by rolling the cathodic roller 14 across the emulsion layer.

In FIGURE 3, the latent image in emulsion layer 12 of the moistened photographic element is developed by pulling the element between cathodic roller 16 and anodic roller 17 so that the emulsion layer is in contact with the cathode and the support is in contact with the anode.

In FIGURE 4, the latent image in emulsion layer 12 is developed by moving the moistened photographic element with the emulsion layer in contact with the stainless steel anode blade 18 and stainless steel cathode blade 19 so that a given area of the moving emulsion surface is first in contact with the cathode and then in contact with the anode.

The power requirements for electrolytic processing depend on the type of emulsion coating, the shape of the electrodes, the electrolyte, and the method used to bring this coating in contact with the electrodes. In the preferred method 80 ampere seconds are required to develop a useful image on one square foot of fully exposed silver chloride emulsion with incorporated developer that has been soaked in a weakly buffered, neutral electrolyte. A

higher image density is obtained without causing excessive fog by using 400 ampere-seconds per square foot. At the other extreme, a pure silver iodide emulsion requires up to 200 amperes per square foot for useful image formation. An applied potential of 440 volts is necessary to obtain this current.

The actual current density at the electrodes depends on the area of the electrode in contact with the emulsion and the duration of thiscontact. In practice the current densities range from 200 to 1000 amperes per square foot (assuming that inch of the electrode circumference Example I A slow silver chloride-gelatin emulsion such as that used for contact printing papers and containing the usual addenda such as spreading agent and antifoggant was mixed with the following solution.

Hydroquinone grarns Ethyl alcohol ccs 40 Formaldehyde 10% solution ccs 32 Sodium bisulfite-formaldehyde gramsa 32 Water to 222 ccs.

To 500 ccs. of the emulsion, 180 ccs. of the above solution was added and mixed at a temperature of 90 F. with vigorous stirring.

This coating mixture was applied to photographic paper support (55 grams per square meter) at a wet thickness of tWo-thousandths of an inch and dried.

A sheet of this paper was exposed by contact with a line negative and then moistened by passing quickly through a bath of cold water.

The moistened paper containing a latent image was then passed through a mangle having two stainless steel rollers. The roller in contact with the emulsion surface was connected to the negative terminal of a 24-volt battery while the other roller was connected to the positive terminal. As the paper passed through the mangle at about one to two feet er minute, development of the image exposed parts of the emulsion layer took place. After passing the paper through the mangle once at the above conditions, the direction of the current was reversed and the print quickly repassed through the mangle whereby the pH of the emulsion layer was lowered and the development reaction stopped.

Alternatively, the same process may be carried out but in which a solution of sodium suliite is used for wetting the exposed paper before electrolytic development. This treatment will avoid the possibility of any oxidized developer stain that might otherwise be formed in the undeveloped areas of the print.

Example 11 A coating mixture was prepared as in Example I but having silver iodide instead of silver chloride and in which one gram of l-phenyl-S-pyrazolidone was added to the emulsion. This mixture was applied to an absorbent paper support such as that used for filter paper and the excess squeegeed off to leave impregnated sensitive paper.

After drying and exposing the sensitive paper, it was moistened with a 5% solution of sodium sulfite and passed through the mangle electrodes as in Example I to produce development. Because of the low tendency of silver iodide to print-out, the prints produced were fairly stable. To some of these prints a reverse current was applied for lowering the pH which resulted in these prints having a further increased stability.

Example III A sheet of silver chlorobromide paper was exposed to a positive image and then soaked in the following solution.

Water to make 1 liter.

This solution was not alkaline and no development took place. However, when the sheet was passed twice through the mangle electrodes in the manner described in Example I a developed and deactivated print was obtained.

Example IV A silver chloride gelatin emulsion was prepared in which was dispersed a solution of 4-phenol catechol and 4-methoxy-l-naphthol in tricresyl phosphate. This emulsion was coated on a partially acetylated fiber base of the type described in US. Patent application Serial No. 786,041 by W. H. Griggs and R. D. Zaffran. The composition of the material as coated was:

Grams per sq. ft. Silver (from chloride salt) 0.16 4-phe-nol cateohol 0.040 4-methoxy-1-naphthol 0.016

A 2-inch x 8-inch strip of this paper was exposed and bathed for two seconds in a solution comprising the following composition:

Potassium chloride grarns 50 Ascorbic acid do 40 Sodium hydroxide do 6 Potassium bromide do 5 n-Butyl alcohol ccs- 50 Water to 1 liter.

Processing speed; 1 ft. per minute 2 Current aimp 0.5

Voltage V0lts 10 Example V An incorporated developer, silver chloride-gelatin emulsion, was prepared and coated as in Example IV except that the developing agent was incorporated directly in the emulsion. The emulsion had the following composition as coated:

Grams per sq. ft. Silver (from chloride salt) 0.16 Hydroquinone 0.23

A 2-inch x 8-inch strip of this coating was bathed in the solution used in Example 1V and electrodeveloped as described in Example IV. An image having high maximum density and low fog was developed on this material under the following conditions of processing:

Processing speed it. per minute 2 Current -amp 0.5

Voltage volts 10 Example VI A silver chloride-gelatin emulsion with an incorporated developer was prepared and coated as in Example IV, except that the developing agent was added directly to the emulsion. The composition of this emulsion as coated was:

Grams per sq. ft.

Silver (from chloride salt) 0.16 Hydroquinone a 0.23 Sodium bisul-fite-formaldelhyde 0.23

A 2-inch x 8-inch strip of this coating was bathed for 2 seconds in a solution comprising:

Sodium sulfate (anhydrous) "grams" 50 Potassium bromide do 2.5 n-Butyl alcohol u cc. 50

Water to 1 liter.

The strip was electrodeveloped as described in Example IV, and an excellent torg-free image of high maximum density was obtained under the following conditions of processing:

Processing speed ft. per minute 2 Current amp 0.5 Voltage volts This material was again processed at a speed of 50 ft. per minute by increasing the current to 4 amps. A legible image with somewhat lower maximum density was obtained under these processing conditions.

Example VII A silver chloride-gelatin emulsion with an incorporated developer was prepared and coated as in Example IV. The composition of the emulsion as coated as:

Grams per sq. ft. Silver (from chloride salt) 0.16 Methyl phen-yl hydroquinone 0.061

Processing speed ft. per minute 2 Current amp 0.5 Voltage volts 12 Example VIII 7 A silver iodide gelatin emulsion with an incorporated developer was prepared as in Example IV. The composition of the emulsion as coated was as follows:

Grams per sq. ft.

Silver (from iodide salt) 0.16 4-phenyl catechol 0.040 4-meth0xy-1-naphthol 0. 16

A 2-inch x 8-inch strip of this material was electrodeveloped as described in Example IV, using the following solution as the electrolyte:

Potassium chloride gran1s 40 Ascorbic acid do 40 Sodium hydroxide do 6 Ethylene diamine tetracetic acid disodium salt do 50 n-Butyl alcohol css 50 Water to 1 liter.

' A good image having low fog was developed on this material under the following conditions:

Processing speed ft. per minute 2 Current amp 1.5 Voltage volts 12 The photographic images developed in Examples IV through VH1 may he deactivated by subjecting them to a second electrolytic treatment in which the direction of current flow is reversed." The. hydrogen ion generated at the anode in contact with the surface of the developed emulsion layer will neutralize any residual alkali that is present, thus deactivating the developing agent and preventing any further development of silver halide.

Variations may be made in the conditions used in the process of our invention. .For example, excellent pictures may be obtained by using the method of Example VI in which the electrolyte solution consists only of grams per liter of potassium bromide instead of the electrolyte solutioiiused, if higher voltages such as to volts are used for the electrolytic step of the photographic process.

The photographic processes of my invention are valuable because they provide a simple rapid method of f min p qtq raph c images in e po d, h e i i e silver halide emulsion layers. My process is especially useful for developing silver images in a photographic 8 emulsion layer containing incorporated developing agent and an electrolyte and is accomplished simply by moistening the photographic emulsion layer and the support and subjecting the emulsion layer to electrolysis in which the emulsion layer is first brought into contact with the cathode and then into contact with the anode. Hydroxyl ions produced by the cathodic action activate the incorporated developing agent and bring about a rapid image development which is then stopped by giving ano'dic treatment to the emulsion layer. In one form of my invention is which the electric current used in the electrolysis flows through the surface of the emulsion layer rather than through the emulsion layer and the support, requires that only the emulsion layer be moistened, thus further shortening the drying step of the process. My process is also useful for rapid development of exposed light-sensitive silver halide emulsion layers containing incorporated developing agent to which an electrolyte solution is applied in the moistening step before the electrolytic step. My process is also useful for developing conventional light-sensitive silver halide emulsion layers which do not contain either an incorporated electrolyte or an incorporated developing agent. In this process the exposed emulsion layer must be moistened with a solution containing the developing agent and electrolyte before the electrolytic processing step or steps. Compared with prior art processes, my process gives prints which may be dried and used much sooner and more conveniently, and avoids the need to use solutions of chemicals in the processing step.

The invention has been described. in detail with particular reference to preferred embodiments thereof but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims. I claim:

1. A process for forming a photographic silver image corresponding to a latent image in a non-alkaline lightsensitive silver halide emulsion layer that contains an incorporated developing agent which requires an alkaline medium for silver halide development, and an electrolyte and is coated on a water permeable support, said process comprising the steps of moistening the emulsion layer and its support with water, uniformly subjecting all of the exposed surface of the emulsion layer to electrolysis in which a direct electric current is passed between a cathode that is brought into contact with the moistened emulsion layer and an anode that is in contact with the moistened support to form a photographic continuous tone silver image in said layer, and subsequently uniformly subjecting all of the exposed surface of the emulsion layer to electrolysis in which the direction of current flow is reversed so that the anode is in contact with V the emulsion layer and the cathode is in contact with the support to stabilize said image.

2. A process for forming a photographic silver image corresponding to a latent image in a non-alkaline lightsensitive silver halide emulsion layer containing an incorporated organic developing agent which requires an alkaline medium for silver halide development, and an electrolyte and is coated on a water permeable support,

said process comprising the steps of moistening the emulsion layer and its support with water, uniformly subjecting all of the exposed surface of the emulsion layer to electrolysis in which a direct electric current at a potential of from five to forty volts is passed between the cathode that is brought into contact with the moistened emulsion layer and an anode that is in contact with the moistened support to form a photographic continuous tone silver image in said layer, and subsequently uniformly'subjecting all of the exposed surface of the emulsion layer to electrolysis in which'the said direct electric current is reversed in direction so that the anode is in contact with the emulsion layer and the cathode is in contact with the support to stabilize said image.

3. A process for forming a photo-graphic silver image corresponding to a latent image in a non-alkaline lightsensitive silver halide emulsion layer that contains an incorporated organic developing agent which requires an alkaline medium for silver halide development, and an electrolyte and is coated on a support, said process comprising the steps of moisteniag the emulsion layer with water, uniformly subjecting all of the exposed sur face of the emulsion layer to electrolysis in which a direct electric current at a potential of from five to forty volts is passed between a cathode and an anode that are in contact with the surface of the moistened emulsion layer in such a way that the exposed emulsion layer is first subjected to the cathodic action to form a photographic continuous tone silver image in said layer and subsequently exposed to anodic action to stabilize said image.

4. A process for forming a photographic silver image corresponding to a latent image in a non-alkaline lightsensitive silver halide emulsion layer that contains an incorporated developing agent which requires an alkaline medium for silver halide development, said developing agent being selected from the class consisting of a hydroquinone, a catechol, a naphthol, a phenol, and a 1- phcnyl-3-pyrazolidone, substituted naphthol, and an electrolyte, said emulsion layer being coated on a water permeable support, and said process comprising the steps of moistening the emulsion layer and its support with water, uniformly subjecting all of the exposed surface of the emulsion layer to electrolysis in which a direct electric current is passed between a cathode that is brought into contact with the moistened emulsion layer and an anode that is in contact with the moistened support to form a photographic continuous tone silver image in said layer, and subsequently subjecting the emulsion layer to electrolysis in which the direction of current flow is reversed so that the anode is in contact with the emulsion layer and the cathode is in contact with the support to stabilize said image.

5. A process for forming a photographic silver image corresponding to a latent image in a non-alkaline lightsensitive silver halide emulsion layer that contains an incorporated developing agent which requires an alkaline medium for silver halide development, said developing agent being selected from the class consisting of a hydroquinone, a catechol, a naphthol, a phenol, and a l-phenyl- 3-pyrazolidone and contains an incorporated electrolyte selected from the class consisting of inorganic salts and including alkali-metal bisulfite-formaldehyde addition complexes, said emulsion is coated on a water permeable support, and said process comprises the steps of moistening the emulsion layer and its support with water, uniformly subjecting all of the exposed surface of the emulion layer to electrolysis in which a direct electric current is passed between a cathode that is brought into contact with the moistened emulsion layer and an anode that is in contact with the moistened support to form a photographic continuous tone silver image in said layer, and subsequently uniform subjecting all of the exposed surface of the emulsion layer to electrolysis in which the direction of current flow is reversed so that the anode is in contact with the emulsion layer and the cathode is in contact with the support to stabilize said image.

6. A process for forming a photographic silver image corresponding to a latent image in a non-alkaline lightsensitive silve halide emulsion layer that contains an incorporated developing agent which requires an alkaline medium for silver halide development, said layer being coated on a water permeable support, said process comprising the steps of moistening the emulsion layer and its support with a water solution containing an electrolyte, uniformly subjecting all of the exposed surface of the emulsion layer to electrolysis in which a direct electric current is passed between a cathode that is brought into contact with the moistened emulsion layer and an anode that is in contact with the moistened support to form a 1Q photographic continuous tone silver image in said layer and subsequently uniformly subjecting all of the exposed surface of the emulsion layer to electrolysis in which the direction of current flow is reversed so that the anode is in contact with the emulsion layer and the cathode is in contact with the support to stabilize said image.

7.. A process for forming a photographic silver image corresponding to a latent image in a non-alkaline lightsensitive silver halide emulsion layer coated on a water permeable support, said process comprising the steps of moistening the emulsion layer and its support with an aqueous solution containing an organic developing agent which requires an alkaline medium for silver halide development, and an electrolyte, uniformly subjecting all of the exposed surface of the emulsion layer to electrolysis in which a direct electric current at a potential of from five to forty volts is passed between a cathode that is brought into contact with the moistened emulsion layer and an anode that is in contact with the moistened support to form a photographic continuous tone silver image in said layer and subsequently uniformly subjecting all of the exposed surface of the emulsion layer to electrolysis in which the direction of current flow is reversed so that the anode is in contact with the emulsion layer and the cathode is in contact with the support to stabilize said image.

8. A process for forming a photographic silver image corresponding to a latent image in a non-alkaline lightsen-sitive silver chloride emulsion layer that contains incorporated hydroquinone which requires an alkaline medium for silver halide development and sodium bisulfiteformaldehyde addition complex and is coated on a water permeable support, said process comprising the steps of moistening the emulsion layer and its support with water, uniformly subjecting all of the exposed surface of the emulsion layer to electrolysis in which a direct electric current is passed between a cathode that is brought into contact with the moistened emulsion layer and an anode that is in contact with the moist support to form a photographic continuoustone silver image in said layer and subsequently uniformly subjecting all of the exposed surface of the emulsion layer to electrolysis in which the direction of current flow is reversed so that 'the anode is in contact with the emulsion layer and the cathode is in contact with the support to stabilize said image.

9. A process for forming a photographic silver image corresponding to a latent image in a nonalkaline lightsensitive silver chloride emulsion layer that contains incorporated hydroquinone which requires an alkaline medium for silver halide development, and incorporated so dium bisulfite formaldehyde addition complex and is coated on a water permeable support, said process comprising the steps of moistening the emulsion layer and its support with water, uniformly subjecting all of the exposed surface of the emulsion layer to electrolysis in which a direct electric current under a potential of twenty four volts is passed between a cathode that is held in contact with the moistened emulsion layer and an anode that is held in contact with the moist support as the emulsion layer and its support is drawn between the said cathode and said anode at a rate of from one to fifty feet per minute to form a photographic continuous tone silver image in said layer and subsequently uniformly subjecting all of the exposed surface of the emulsion layer to electrolysis in which the direction of current flow is reversed so that the anode is in contact with the emulsion layer and the cathode is in contact with the support as the emulsion layer and its support is drawn between the cathode and anode at the rate of from one to fifty feet per minute to stabilize said image.

- 10. A process for forming a photographic silver image corresponding to a latent image in a non-alkaline lightsensitive silver iodide emulsion layer that contains incorporated lphenyl-3-pyrazolidone and which requires an alkaline medium for silver halide development, and is coated on a water-permeable support, said process comprising the steps of moistening the emulsion layer and its support with a water solution of sodium sulfite and uniformly subjecting all of the exposed surface of the emulsion layer at electrolysis in which a direct electric current is passed between a cathode that is brought into contact with the moistened emulsion layer and an anode that is in contact with the moistened support to form a photographic continuous tone silver image in said layer.

11. A process :for forming a photographic silver image corresponding to a latent image in a non-alkaline lightsensitive silver chloride emulsion layer that contains incorporated 4-phenyl catechol, 4-methoxy-l-naphthol in tri-cresyl phosphate and is coated on a water-permeable support, said 4-phenyl catechol and said 4-methoxy-1- naphthol requiring an alkaline medium for silver halide development, said process comprising the steps of moistening the emulsion layer and its support with water containing potassium chloride, ascorbic acid, sodium hydroxide, potassium bromide and N-butyl alcohol, uniformly subjecting all of the exposed surface of the emulsion layer to electrolysis in which a direct electric current under a potential of ten volts is passed between a cathode that is brought into contact with the moistened emulsion layer and an anode that is in contact with the moistened sup port to form a photographic continuous tone silver image in said layer and subsequently uniformly subjecting all of the exposed surface of the emulsion layer to electrolysis in which the direction of current flow is reversed so that the anode is in contact with the emulsion layer and the cathode is in contact with the support to stabilize said image.

12. A process for forming a photographic silver image corresponding to a latent image in a non-alkaline lightsensitive silver chloride emulsion layer that contains incorporated 4-phenyl catechol, 4-methoxy-d-naphthol in tri-cresyl phosphate and is coated on a water permeable support, said 4-phenyl catechol and said 4-methoxy-1- naphthol requiring an alkaline medium for silver halide development, said process comprising the steps of moistening the emulsion layer and its support with water, uniformly subjecting all of the exposed surface of the emulsion layer to electrolysis in which a direct electric current under a potential of ten volts is passed between a cathode that is held in contact with the moistened emulsion layer and an anode that is held in contact with the moist support as the emulsion layer and its support is drawn between the said cathode and said anode at a rate of two feet per minute to form a photographic continuous tone silver image in said layer and subsequently uniformly subjecting all of the exposed surface of the emulsion layer to electrolysis in which the direction of current flow is reversed so that the anode is in contact with the emulsion layer and the cathode is in contact with the support as t the emulsion layer and its support is drawn between the said cathode and anode at the rate of two feet per minute to stabilize said image.

'13. A process for forming a photographic silver image corresponding to a latent image in a non-alkaline lightsensitive silver chloride emulsion layer that contains inconporated hydroquinone and sodium bisulfite-formaldehyde addition complex and is coated on a water-permea ble support, said hydroquinone requiring an alkaline medium for silver halide development, said process comprising the steps of moistening the emulsion layer and its support with a water solution of potassium chloride, potassium bromide and N-butyl alcohol, uniformly subjecting all of the exposed surface of the emulsion layer to electrolysis in which a direct electric current under a potential of seven volts is passed between a cathode that is brought into contact with the moistened emulsion layer and an anode that is in contact with the moistened support to form a photographic continuous tone silver image in said layer and subsequently uniformly subjecting all of ii? the exposed surface of the emulsion layer to electrolysis in which the direction of current flow is reversed so that the anode is in contact with the emulsion and the cathode is in contact with the support, as the emulsion layer and its support is drawn between the said cathode and anode at the rate of two feet per minute to stabilize said image.

14. A process for forming a photographic silver image corresponding to a latent image in a non-alkaline lightsensitive silver chlorobrornide emulsion layer coated on a water permeable support, said process comprising the steps of:

(l) moistenin-g the emulsion layer and its support with a solution containing sodium sulfite, hydroquinone, methyl-p-aminophenol sulfate and potassium bromide, said hydroquinone and methyl-p-aminophenol requiring an alkaline medium for silver halide development,

(2) uniformly subjecting all of the exposed surface of the emulsion layer to electrolysis in which a di- .rect electric current under a potential of 24 volts is passed between a cathode brought into contact with the moistened emulsion layer and an anode that is in contact with the moistened support to form a photographic continuous tone silver image in said layer, and subsequently uniformly subjecting all of the exposed surface of the emulsion layer to electrolysis in which :the direction of current flow is reversed so that the anode is in contact with the emulsion layer and the cathode is in contact with the support to stabilize said image.

15. A process for forming a silver image corresponding to a latent image in a non-alkaline light-sensitive silver halide emulsion layer in the presence of moisture, a developing agent that requires an alkaline medium for silver halide development, and an electrolyte, said process com prising the electrolytic step in which a continuous electric current is passed through said electrolyte to a cathode, said cathode being contacted uniformly with all of the moistened and exposed surface of the emulsion layer to release sulficient hydroxyl ions to activate said developer and cause development of said silver halide and form a photographic continuous tone silver image in said layer.

16. A process for forming a silver image corresponding to a latent image in a non-alkaline light-sensitive silver halide emulsion layer in the presence of moisture, a developing agent that requires an alkaline medium for silver halide development, and an electrolyte, comprising:

(1) an electrolytic step in which a continuous electric current is passed through theelectrolyte to a cathode, said cathode being contacted uniformly with all of the moistened and exposed surface of said emulsion layer to release sufficient hydroxyl ions to activate the developer and cause development of said silver halide to form a photographic continuous tone silver image in said layer, and

(2) an electrolytic step in which said electric current is reversed to convert said cathode into an anode and release suflicient hydro-gen ions to inactivate said developrng agent and stabilize said silver image.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Grieg: Proceedings of the I.R.E., October 1948, pages 1224-1235.

enial No. 338,261, Rzymkowski (H.P.C.), published June 1,1943. 0 

1. A PROCESS FOR FORMING A PHOTOGRAPHIC SILVER IMAGE CORRESPONDING TO A LATENT IMAGE IN A NON-ALKALINE LIGHTSENITIVE SILVER HALIDE EMULSION LAYER THAT CONTAINS AN INCORPORATED DEVELOPING AGENT WHICH REQUIRES AN ALKALINE MEDIUM FOR SILVER HALIDE DEVELOPMENT, AND AN ELECTROLYTE AND IS COATED ON A WATER PERMEABLE SUPPORT, SAID PROCESS COMPRISING THE STEPS OF MOISTENING THE EMULSION LAYER AND ITS SUPPORT WITH WATER, UNIFORMLY SUBJECTING ALL OF THE EXPOSED SURFACE OF THE EMULSION LAYER TO ELECTROLYSIS IN WHICH A DIRECT ELECTRIC CURRENT IS PASSED BETWEEN A CATHODE THAT IS BROUGHT INTO CONTACT WITH THE MOISTENED EMULSION LAYER AND AN ANODE THAT IS IN CONTACT WITH THE MOISTENED SUPPORT TO FORM A PHOTOGRAPHIC CONTINUOUS 